The person working in a secure laboratory in Atlanta may have come into contact with a small amount of a live virus, CDC spokeswoman Barbara Reynolds said in an emailed statement. The experimental material was on a sealed plate, but wasn't supposed to be moved into the lab in which the technician was working, Reynolds said. The worker will be monitored for 21 days and the person's name hasn't been released.

Additional employees have been notified, but none has required monitoring, Reynolds said. Other staff will be assessed for exposure.

There is no risk to the public and lab scientists notified CDC officials of what happened on Tuesday, Reynolds said. The lab has been decontaminated twice, and the material in question was destroyed before CDC officials became aware of the mistake.

The possible exposure is under internal investigation and has been reported to Secretary of Health and Human Services Sylvia Burwell, Reynolds said.

Transfers from the lab the experiment material came from have been stopped during the internal review, and the lab the exposure may have happened in is closed, Reynolds said.

The technician's potential exposure is at least the second to prompt a precautionary response from the agency in six months.

In June, at least 52 workers at the CDC took antibiotics as a precaution because a lab safety problem was thought to have exposed them to anthrax.

News of the technician's possible exposure to Ebola comes days after CDC Director Tom Frieden returned from West Africa, where an outbreak of the virus has killed thousands. Frieden said Monday that response to the outbreak has improved significantly in recent months, but the virus continues to spread in Monrovia, Liberia and Conakry, Guinea.

Public health officials have said Ebola spreads through direct contact with the bodily fluids of someone who is infected with the virus — putting health care workers and those in close quarters with infected people at higher risk of contracting the virus. Four health care and aid workers who contracted the virus have been treated and released from Emory University Hospital in Atlanta.

In a statement, Frieden said he's troubled by the technician's potential exposure and the CDC has worked to improve safety protocols as it helps respond to the outbreak in Africa.

"I have directed that there be a full review of every aspect of the incident and that CDC take all necessary measures," he said.

The CDC plans to publish a report on what happened, Reynolds said. It is also planning to report the potential exposure to an external advisory committee that offers advice on best practices in lab science and safety.